Fluid-pressure operated device



FEB. T6, 1954 a. OLAH 2,6 69;247

FLUID-PRESSURE OPERATED DEVICE v Filed March 11, 1950 7 9 Sheets-Sheet 1 INVENTOR GEOR GE OLA H -BY zzyw PM A TTO/QNE YS Feb. 16, 1954 G. OLAH FLUID-PRESSURE OPERATED DEVICE 9 She-fs-Sheet 2 Filed March 11, 1950 II; VII

. FIGLA A n I I. a.

FIG.7

[.NVENTQR GEORGE OLA-H A TTOKNEYS Feb- 16, 1954 G. OLAH,

FLUID-PRESSURE OPERATED DEVICE 9 Sheets-Sheet 3 Filed March 11, 1950 S H Y T%: TL N m w v T m wr 6 WW My 3 Feb. 16, 1954 OLAH FLUID-PRESSURE OPERATED DEVICE Filed March 11, 1950 9 Sheets-Sheet 4 lllllllll /l////// /////l l/l/l/l/ IIIIIII-lllnll INVENTOR GEORGE OLAH J/l/l/l/ll/ ATTORNEYS Feb. 16, 1954 Filed March 11, 1950 G. OLAH 2,669,247 FLUID- PRESSURE OPERATED DEVICE 9 Sheets-Sheet 5 I83 I 20?. I74

IN YEN TOR 6 E ORGE OLA H H TI'ORNEY Feb. 16, 1 954 G, OLA 2,669,247

FLUID-PRESSURE OPERATED DEVICE Filed March 11, 1950 9 Sheets-Sheet 6 FIG. 12,

mVEN TOR GEORGE 'oLAH A T'TOR NE YS Feb. 16, 1954 I OLAH 2,669,247

FLUID-PRESSURE OPERATED DEVICE 9 Sheets-Sheet 7 Filed March 11, 1950 A TTORNEYS &

GR \l 245 mvE/vroR 15 GEORGE OLAH Feb. 16, 1954 G. OLAH 2,669,247

FLUID-PRESSURE OPERATED DEVICE' Filed March 11, 1950 v e-sheet-sheet a /NVEN TOR GEORGE 0L A H A r om/5 Y5 Patented Feb. 16, 1954 U I D JRE'SSURE OPERKTEDDEVTCE Geerge 012th, mending England} assignbr to flre cision -nevclopments -(lomiuiny Iaimited; Lon

don, Englfind, vet co'mpanyi ofi-Greart Britaim AfiIflicaJtiofiMreh 11, 19511, seriammrmosc- 'fihisdnvention relates to fliiid -pressiire oper kt ed devices 2115 has forit's' main object t6" brovide' m'eane wherebyforces of veirying magnitudes may he' translated into coriespdndir'ig li vm m'g soon; into forces-of"varyingmagriitud'es vvli'ich niytfien tie tmnsittd ihto pressur'e -orpresgure differences." Yetf anotfierofiject istfie provision ofsuch converting means in ai'fbrm whichwill result in arsubstaz'ntiai amplificationiof the power 'level of 'tl'ie" originalsignals'.

According. to the present invention, memi'sifbr vamngwfie 'pre'ssure of'ai flhid as a fiinction" of tfie value of' a variable forceeomp'rises a duct morning. (01. 137-845)?" operatiiigwith the-seatin andur ewawayfrom 'tjh'e sameun'der the action ofthefliigher' of'the two tpressures alreadyreferredtb; 'zi'nd means-fur afip'plying'tlie varivblef'orcetbtheballl'inthetsense the urging *it" into sealing 'c'ontatit "With"t1'ie concd seating; V

understood, there-win now*'b'edescribed various to roduce a pressu'redifferentia proportional area b'e'm'e'aJSiireIi-E i21 5 1s a s'ectibnalside elevationof am apps ratus embodying the invention and intendetl to produce" a*pressure prqpdrtionaito a rate of flow, -Figfl6 is ZflfiOIiif lGVEfiCfl of this apparatus wi TisGifiepEtr'tsshGWn' in se'ctio'n;

is e2 fragmentary View of part: ('J'Jf-- "the ap'p'arit'iis shownin Figi 6 as modifiedfbfproducin'g' aF-pressu-redifference m-ozsbrtibnar-te the fate o'f "fiow 'to-b'measured; *"Fi g'I 8 1samagrammatic s'titidnal e lvaifig'n illustrating one means -which'maybe 'em pmyewfor fionve'rtin'ga-disp1ace'ment-" into j a force L which is lto'be ieinmdy'edin" eelppairatusfiofthe invention fbr'producin a opoitional'fluid pressure; H g: .iis-a; sect'ion' taken orr'the line O'f-Fiig; 11 95nd showing" a" device fbr*c0nvertin'g an electricsig'ri'aJ-l into" a forceandtherr int'b a proportional pressuredifieren e,

F'gf 10 15a plan View attire-apparatuswith 1511 top cover removed; 11'- is a section talkeflonthe line 12 i'sfan elevationql view-taken from"the left of Figf.9* with" parts broken awaiy'and' other "parts -'sh gwn m section; v

Fig. 1 4 is a diagrammatic view illustrating means fo'r"convertinga"displacement into an electric"signa1w1iioh'i's to-b'e cozw'ertecl i'n an appw ra tus according' to Figs. 9-12 into a; proportional pressure difference,

Fig: 15 a diagrammatic sectional elevation illustrating" the manner in which two of media V1665 :fo'r producing a prm'oortional pressure diff'rehcein accordance witlrthe invention-maybe connected in cascade;

'Fig: 1 6 is" a; diagraminatibsect ibnal elevation illustrating a device according to the invention provided? with feed-back means, .Filgi 1'7 isa'sect'iOn takenion' the line ofF'ig"; 1'8 and showing a device-utilising the basic means according to the irivention in order to produc a" pres ure-Havin a: predetermin'eii' but variable":relationship to" a. control pressure; 7 r

QE i 'g; IBis a section taken on the 1in"e"X VIiI XVIII ofFlg. 17;

frii'g'z19iewsectien'takenonthcmreXIX XIX Broken-awayjta'kcn fium the left o'fFig'. 1'7, t i

Fig. 21 is a section taken on the line XXI XXI of Fig. 19,

Fig. 22 is a section taken on the line XXII- XXII of Fig. 21, and

Fig. 23 is a fragmentary section taken on the line XXIII-XXIII of Fig. 19.

Referring first of all to Fig. l which illustrates the basic device according to the invention, i indicates a duct through which a gaseous fluid is supplied at a predetermined pressure to a restricted orifice 2 which delivers into a chamber 3 having an outlet at t. The outlet is flared to constitute a coned valve seating 5 with which is adapted to co-opcrate a ball valve 6 which is supported by an abutment 1 to which a variable force is adapted to be applied in the direction in dioated by the arrow 8.

pressure responsive device (not shown).

In the example considered, the pressure of the gaseous fluid supplied through the duct l is higher than the atmospheric pressure, the outlet end of the valve seating 5 being in communication with the ambient air.

The pressure in the chamber 3 when the outlet opening l is closed by the ball valve 6 being urged into contact with the seating 5 under the action of the force applied to the abutment l, assuming that the pressure responsive (or pressure actuated) device connected to the outlet passage 9 the like in which the apparatus is set up and the ball valve is such that when fully open the resistance it olTers to the flow of fluid through .the opening 2, 5, is one-ninth of the resistance to the flow of the fluid through the constriction .2 In this case, the minimum pressure in the chamber 3 is one-tenth of the predetermined super-atmospheric pressure prevailing in the duct i.

should the pressure responsive device connected at the passage 9 consume pressure fluid,

the maximum pressure obtainable in the chamber 3 feeding the same will be reduced to a degree depending upon the external resistance of this device and if the latter can feed fluid back into the chamber 3, the minimum pressure obtaina'ble therein will be increased. In other words, the extreme or saturation values of the means according to the invention will be brought closer together. Nevertheless, any value for the pressure in the chamber 3 intermediate these saturation values can be obtained for appropriate positions of the ball valve 5 between fully closed and fully open.

" It will be understood that the fluid under pressure seeking to flow from or into the chamber 3 fitted with the valve controlled opening 4, 5, by way of the latter produces a force acting on the ball 6 which tends to open the valve. Should this force be smaller than the instant value of the variable force applied to the abutment 1 in the direction indicated by the arrow 8, the latter force urges the ball 6 towards its seating 5 so that Into the chamber 3, there opens an outlet passage 9 leading to a l the fluid pressure acting on the ball will increase in value. When a position of equilibrium is reached, the pressure in the chamber 3 is proportional to the value of the variable force, the ratio of pressure to force being constant and independent both of the predetermined pressure maintained in the duct l and of the rate of consumption of pressure fluid by the pressure responsive device connected at the outlet passage 9, provided that the proportional pressure is within the saturation values referred to above.

In order to get the best results, the included angle of the conical surface of the coned seatin 5 for the ball 6 should be relatively small, that is to say, in the range of 20 to 40. The preferred angle is 30.

In order for the ratio of pressure to force to be constant, it is necessary that the effective area of ball 6, acted upon by the pressure in chamber 3, be substantially constant. It has been found in practice that this requirement is met to a high degree of accuracy when the included angle of seat 5 is in the range of 20 to 40, preferably 30. If the angle is too small, the ball can sometimes jam in the seat. If the angle is too big, the flow of air through the gap between the ball and the seat becomes turbulent and unstable instead of laminar, resulting in more or less random fluctuations of air flow.

Where the variable force may assume both positive and negative values, it is preferred to employ two of the means according to the invention and to arrange that the variable force acts on both balls, but in opposite senses on each of them. The pressure diflerence between the two ducts fitted with the valve controlled openings, which pressure diiference may assume a positive 'or negative value, is then proportional to the value of the variable force. A simple arrangement of this character will be described with relation to Fig. 4, for example.

Such an arrangement has an inherent negative damping which makes it oscillatory and makes it difiicult, if not impossible, to secure equilibrium conditions with a linear relationship between force and pressure over the whole range. This negative damping may, however, be compensated for and the arrangement stabilised by the provision of positive damping means acting on the part or member through which the variable force is applied to the ball valves, see for example Fig. 4. Suitable damping means include dash-pots as shown in Figs. 4 and 6 or eddy current devices such as metal elements located in the field of a magnet (as shown for example in Fig. 9). When such damping is applied, the oscillation of the arrangements referred to can be prevented and a substantially linear relationship between the variable force and the pressure diiference produced may be secured.

Without the positive damping, the arrangement may be used as an oscillator for producing fluid pressure pulses. It has been found that the relationship between the variable force and the mean pressures produced in the arrangement n. linear at both ends of the full control range but that the slope is reversed near the zero point. A response of this character can be employed for operating controls having a snap-over action.

Various examples of the way in which the invention may be utilised in practice are illustrated in the accompanying drawings and will now be briefly described.

. In the example shown in Fig. 2, the variable force which is to be converted into a fluid pressureisiappliedr o-a lever In which ise pivotedgon alfixed support at. II andrhasfiecllred thereon at one.- endpanl abutment, I for operating-upon aaballvalve I3 'Theaball -valveiisa free-ball adapted. toseat in the conical mouth ML of a duct I5, leading, into a chamber- I6, which; is supplied at-the. opposite-end through ,a restricted orifice, '37, from a. source. of. compressed @air. inot shown) by way, ofoa duct 1 B and..hasv ani-outlet I iLleadin'g L to a. device; capable-oi responding; to fluid, pressure 'Sucha d'eviceiin; its simplest form; maybe a pressure;gaugetzfl as shownrin Fi '2, of; the, indicating or recording: type but it, is .to. be understood that the-deviceimay also be; .acservo motor or the-alike. Y Itz isr convenient to,.arranget.thevl terminal I portionrorthe duot It with ,its ,axis: vertical and: to have; tiller-conical mouth, .I'Lat thezlower endlof thee-chamber: I5 as; illustrated,- the included? ansla ot. the cone generally. being-about 30. -.The ball I3: rests-Jon theabutment t2 and; the ,variable force. applied, to,. the lever I It .in the; sense for causinggthe abutment to urge the-shallinto-sealing engagement with the conical seating; 14a

The. example illustrated: is ,adapted to: derive the variable force-(from a-upress-urewhich isl-of smallhmagnitude such. as: may; be encountered ior example, in draughtcontrol apparatus: TwQ-bells 21 andi22'are fixedoneaat eachend ofethetoperating lever I [I by rods 23,1and:24 respectively, and clip; by their lower edgesinto a, body ofliquid 25,..c0n'tained ina-suitable: tank 26 and" forming aaliquid sealfor, therlower ends of the bells. 2?! {indicates alpassagerthroug -h which agaseous fluid, flows 1inltheadirectionzindicated by the arrowI 2,8, a. controlling; orabutterflyvalve 279 being located n thea-passage -tocontrol the flow of the gaseous; ifluid through the .latter. The space within. the hell 2 I is placed inrcommunication with the interion-of the passageufl at a point in advanceaof the .v-alve ma wayof a. duct 30,- whereas the space within.; the bell! 32* isplaced in .rcommunication with the-passage: 21:21; a point atw the .rear of the valve-291 by way of a: duct 3 I i The pressure difference .:between1portions;of the-passage 2] at opposite sides: of :thevalves29 isiofasmall magnitude, -as will be understood; However, these pressuresvacting on:the ;bells-.-2l and 22s produce: a variableresultantmforce on the.,lever, l (Lwhich in turn operates through :the' ahutment- I2 uponthe ball valve] 3;;to4-cause the production in theipassage I El-leading to" thevgpres suresgauge 2&- of ar-pressure proportionalltothe value of the variable-force. v i

- 1n the -aoperation of this device, :airat apre-t determined pressure is supplied through 1711651111013 I8i-to the inlet end of the-restricted orifice I'Iand aaprcssure .:builds up within the passage I'91-leadin mlo then ressuregauge 20; Whenthe pressure of the air in the passageireaches a certain value, the-ball .is urgedaway from its "seating due it'ol thefact that the downward force'exerted on itherball, overcomes i the upward force exerted on :thesball due to the action of the variable force applied to: the lever I0. -Ase'the ball leavesiits a isimpler matter. with an 1 arrangement of this character-to, produce 1 in the ,a passage, leading to.

the pressure-gauge, a pressurewhichi is.-,.several hundred times: the pressure. difierence which. is available in the passage 2.1-.

It will be-understood-thata similar arrangement may-be employed: where the pressures to bemeasured or recorded are relatively high. -In this-case, see. Fig.3, thebell-ctype pressure detectorsmay beireplaced by detectorslli'z and 33 oithe-bellowsor Bourdon-tube type.- As the;v full range oi: displacementof-theball valve. I3 is extremely small, the corresponding displacements OfthepressureTdetectors 32 and 33 are also small so-Lthatflthe,infiuencevof the elastic properties-of the :materials, from which the 1 detectors. are .-con-. structed upon the accuracyof the result becomes ne li ible. I

in the-examplesoh-fai-pdescribed, it has been ass-question of converting-a variable force into a proportional pressure, but. it .is also possible". to convert a variable force into a proportional pressure (difference, this being of particular importan-cc the-casewhere, the force may assume both positivevand negative values. Alsimp-le ex-.- ample of, apparatus for this purpose is shown in Fig. l w-here .two apparatus, each identical with that showngin Fig, 1, are arranged in opposition; Inw thiscas -compressed air, is: supplied by way of arpipe-fl t to-oneapparatusscomprising a; duct 35; restricted orifice 36, chamber 3.7. and outlet 38 with, conical seating 39- and a branch pipe 40 from the. pipe 34 supplies'thezcompressed-airto the other apparatus comprising a. duct- 41, .restricted orifice 42, chamberldt' andioutlet M with conical valve seating d5. A ball 46' is provided to .co-operate with the seating 39; and another ball His provided to-cot-operatewith-the seating 45, a single abutment 48 being vdisposed between the two balls toact: uponieach of theme atthe same time. Thisabutment is carried atone end of a lever49 which-is pivoted onatfixed support attic and is-ladaptedito havethe forcetobe measured app-lied to itsiother free end as indicated by the arrow 51. The chambers 31 and 43-have outlet passages 52 and 53 respectively whichcommunicate with the, appropriate ends of a..U-tube manometer 54. For the reasons mentioned above; a positive damping device is provided in association'with the lever- 49; this being'shown diagrammatically as a disc or paddle 55 arranged to workin a bodyfifi of liquid held in a container 51, the disc orpaddle being connected to the lever 49 b-y means of arod 58.

It will-be-seen-that the one ball valve 46 1s oppositely located'tolthe-other 4'1, that is to say, so-that axial movement of the abutment 48. will permit'one vhall valve to move away from its seat-- mg -while urging the other ball valve onto its, seating. Whena pressure is exerted upon-the lever -49-,. in the direction indicatedtby the. arrow 51, the abutment 48 tends to move upwards and this-movement isiassisted-by the pressure acting. upon the 'ball :valve 46 and resisted bythe pressure actingl-upon the ball valved-I. It willvbe reached in 'which the difference between the press sures in the two passages 52 and 53:is-pro.por-- tional to.the valuelof the:force applied at fil, instead ot-beingconnected to a pressure responsive deviceaof the character. indicated,v their pas.- sages; 521and53- may bearrangedto. supply the opposite, ends. of avvdouble-acting cylinderlof a servomotorl or. be connected to some other pressure-actuateddevice;

' The exampleswhich have been desorihedabovehavefbeen' ofgpressurel-toepressuret conversion but it is also possible to have displacement-to-pressure conversion arrangements. For example, an element which is subject to a variable degree of displacement may be connected to one end of a resilient member, the other end of which is connected to an abutment for operating upon the ball valve or valves of an arrangement such as has been described. In this way, displacement of the element is utilised to produce a force acting upon the ball or balls which is proportional to the displacement of the element.

A practical construction of such an arrangement is illustrated in Figs. and 6. In this case, the displacement to be converted is that of a float 59 supported by the mercury (not shown) in one leg '50 of mercury manometer tube, part of the other leg of which is shown at (ii in Fig. 6. As shown in Fig. 5 the float 59 has secured thereon a rack bar $2, the teeth of which are in mesh with those 01" a pinion 63 secured on a spindle 64 which suitably supported for rotation and carries at one end a U-shaped permanent magnet 65, the poles and iii of which are located in the annular gap between the interior surface of a sheet metal housing $53 and the external surface of a re-entrant cup-shaped portion 69 of a closure member 'Ill secured in the open end of a branch li extending from the tube til somewhat to one side of the axis thereof. The closure member IE is held in place by a suitable clamping ring #2 and bolts "it with the interposition of a packing ring it so that the end of the branch II is closed in a pressure-tight manner. Over the open end of the recess 5 in the closure member It is secured a guide element it having a central axial bore 'ii' through which extends with some clearance a spindle it which rotatably mounted at one end in the inner end wall or the recess '15 and at the other end in a front plate IS. Within the recess '55, this spindle it has secured thereon a bar 80 of magnetic material which is disposed between the poles 65 and iii of the magnet 65. It will be understood that the re-entrant portion of the closure member it is of non-magnetic material with the result that any rotation of the magnet 55 about the axis of the spindle 64 will cause a corresponding rotation of the bar 89 with the spindle it which is secured thereto.

The front plate 59 is supported by suitable spacer members 8! from a rear plate I32 which is in turn secured to a base member 83 supported from the tube til in the manner indicated. A removable cover having an inspection opening covered by glass window is secured on the base member 83. A spindle 36 is rotatably mounted between the plates I9 and 32 to extend parallel with the spindle l8 and secured thereon a lever all of bifurcated construction which has a roller 58 rotatably mounted upon a spindle 88 that extends between the two limbs of the lever 8'! towards the free end of the latter. There is secured on the spindle 18 a earn as shaped according to the square root law and adapted to support by its edge the roller 85 carried on the lever 81.

Also secured on the spindle 836 is a. further and shorter lever SI which is formed towards its free end with a longitudinally extending slot 32 along which may be adjusted an anchoring block 93 for one end of a helical tension spring es, the other end of which is anchored to a block Q5 carried near one end or a balanced lever st to be referred to below. The anchor block 93 has a stud 91 extending laterally therefrom and slidably engaged in the slot 92, the block being retained on the lever 9| by a nut screwed on the end of the stud. Adjustment of the block 93 along the length of the lever SI in order to vary the lever arm at which the force clue to the spring may be applied is effected by means of a screwthreaded spindle 98 which is rotatably but nondisplaceably mounted in a block 99 secured on the spindle 8B and has its screw-threaded end threadedly engaged in a correspondingly screwthreaded aperture I09 formed in the anchor block 93. For zero adjustment purposes, there is secured in a block Iill mounted on the spindle 88 a screw-threaded spindle I02 projecting beyond the spindle 86 to receive an adjustable weight ms which is adapted to be screwed, along the spindle I02 as required and then to be locked in position by tightening a screw I94 in order to draw a thin end portion I03a of the weight I03 towards the main body of the latter and thereby to cause the screw-threads in the two portions of the weight to bind irictionally upon the screwthreads of the spindle I62.

Referring now to the balanced lever 96, this is provided at the centre of its length with a block I05 by which it is pivotally mounted between a pair of upstanding lugs I86 formed on a block It? which is secured to the lower edge of the rear plate 62. The pivots for the lever 9d are shown at H38 in Fig. 5. At the end adjacent to the block 95 to which the spring 94 is anchored, there is attached to the lever a. projecting screw-threaded spindle IE9 upon which is adjustably mounted a balance weight IIil adapted to be adjusted and locked in position in the same way as the weight I03. 33a already referred to. At the opposite end of the lever 95 is secured a cup-shaped member III which is adapted to work with slight clearance over a disc H2 secured in the adjacent end of the upper face of the block Iil'I. The parts III and H2 co-operate to constitute an air dash-pot. Also mounted on the lever, one at each side of the pivotal axis or" the latter, are two abutment members II 3 and H4 which are adapted to cooperate with ball valves of two arrangements substantially in accordance with Fig. 1 which are mounted in the block Ill'i.

This block is formed with a vertical bore H5 leading from its lower face into a horizontal bore II 6 which is intersected at either side of the bore H5 by a vertical bore II! or H8, opening into the upper face of the block It'I and leading at its lower end to a stepped passage H9 or I20 respectively which opens into the bottom face of the block. In each of the bores Ill and H8 there is secured a cylindrical plug IN, or I22, respectively, having an axial bore I23, or I24, which is formed at its upper end with a conical seating I25, or I29, adapted to receive a ball valve I271, or I28, co--operating respectively with the abutments H3 and IE4. Each plug I2I or I22 is formed with a radial bore I29 or I38 at a level such that it can be brought into register with the horizontal bore H8 when the plug is fixed in position. When, as is the case in the example shown in Fig. 6, the apparatus is intended to produce as an output a proportional pressure, only one of the plug and ball valve combinations is rendered operative. Consequently, the plug 42! is shown positioned with the radial bore I29 turned out of register with the bore H6, whereas the plug I22 has its radial boreIBt disposed in register with the bore IIG to establish communication between the latter andiftheaxial bore I'24iin the; plug. .Q In thiscase the'restrictedm'ifice necessary for the purposes.

'tdthe'ibores -II and H6. Similarly, in the stepped passage I there. is secured; the end of an outletpipe" I33"by way of which the prop'or-,. tionai 'pressure'produced the apparatus may be led away-to a pointat which it is to be utilised,

for "examplato a fiuidpressure' operated device.

adapted to control, the "rateiof fflow being measuredgby'themanometer 60:6! or .to produce at a distantpoint. anindicatiori ;of such rate of flow.

It is preferred, as indicated in Figs..5 and '6; that branc'hzpipes I34 'and1l35 "be connected to the pipes I32 and" I33 1 respectively, these branch p pes being-connected to pressure responsive dev ces (of WhiCh OI1B"COIl11GCtEd to the pipe I34 is indicated-at 135 "in Fig.5) mounted in apertures.

in'the l'ower'end of the .front plate :19 "so that theindication produced.bythedevice in question.

may be observed'through the window. 85;

In the nperationtof the apparatus illustrated in Figs-., 5 and 6', the float '59 rises or falls in accordanceywit'hthe changes in the. rate of flow beingmeasuredin the mercury manometer til,

BI and-throughthe'rack 62 and pinion 63 causes appropriate .rotation' of the magnet 65. The poles. '66 and 61 "of this magnet, by. their influe ence'on'the'bar Iwfcause a corresponding rotation-'of the spindle 18 withthefoam 95 so that the free endof' the lever-"81 .will be raised or lowered accordingly; Infconsequence, the spring 94 .will

be'tensionedzto'agreater 'orrles'ser degree and,

It will beunderstoodthaltthe weights I03 and... III) ,mayqbe' moved along the. screw-threaded. spindlesv I02. and "19in order to adjust thetappa ratus, for 'example ,'in order. to adjustthe zero.v

setting thereof. Adjustment of the anchor block 93 for the uppe iend of the spring94 maybe utilisedin lorderto varyathe. ratio of the trans? missionlfrom thelcam 90,.it0 the'balancedv lever 96 and the .air dash-pot. l l I. and .II 2 provides, as will be understood, thenecessary positive damp:

When, as .in some-cases is desired, it is pre ferred' that theoutput of thelapparatus be a..dif-.. ferentialpressure proportional. to 'the' .displace.-.

ment of the float 59,'thefapparatus maybeflmodkc fled in the'sense indicated in Fig '1. ICorresponde ing. parts in this figure aregiven the samerefr, erence numerals as in Fig. 6 It will be seen that bothabutments 'II3"'and. II4 on the'lb-alancedlever 96 are here operative since the.plug.I.2I has. been .turned about its axis .througli. l80v in order to bring its radial'bore I.29"into register with'ithe. corresponding end. of theLhorizontal; bore I I5..

Since now both'devices are operative, theicone striction' I'3I,"shoWn in 'Fig., 6, is removed from.

the .bore. II5 and,separateiconstrictions I3ia and.

I3Ifb :are provided. in thebore. .LI 6 at either sideof the junction of theglafiter'withltherlzelttic'al,.l

bore H5. In addition, an outlet pipe I33a; se-

cured inthe stepped aperture lid-which com municateswith the bore receiving the plug member. 'I'2I. The manner of operation of the apparatus as thus modified willbe clearlyunderstood without further description.

. Another method of securing displacement-Ito'- pressure conversion is diagrammatically shown. in '.Fig-. v8. In this case, the abutment I31 for I acting upon the ball valve 1380f a basic'device, 10

such as" is illustrated in Fig. 1, is carried by a lever I39 .which'is pivoted .at I40 and has a sliding or.rollin"g weight member I4I mounted -on its uppersurface and adapted to be displacedby means of a connection I42'in one or otherof'the 15 directions indicated by the arrows. By "means of .the .connection. I42; the weight member I4I"is operatively connected to a displaceable element. the movements 10f which are .to .be converted'into'. a proportional. pressure. It willbe clear that any] displacementof theelernent. will move the weight I member I4I.along .the lever. I38 toproduce' a corresponding variation of leverarm ratio'andthereby a corresponding variation in .ithebforce. which 'is applied to the ball I38 by the. abute. ment [31.

The invention may 'alsobe utilised for the con version of electric'signals to'a proportional-pressure or' pressure difference. For this purpose, the electric, signals maybe fed into'the winding of a solenoidor, asispreferred, into the winding'of a moving coil disposed ina magnetic field,- the arrangements being such that the electric signals are. utilisedto'producea force proportional thereto, which force may then be. applied to the ballvalve of an arrangement'su'ch as is shown in Fig; 1 orto'the .twoball-valve's oiian arrangementsuch' as is shownin'FigA. A practical" example of'an' arrangement. of the latter character is illustrated in Figs. 9 to.12..

In .these figures there is shown a pot-type permanent magnet composed. of a central tubular core I43 of soft 'i'ron secured at its' upper end in an aperture in a top member I44 and having-its" lower end.I45 constituting a pole piece located with adequate clearance in an aperture I46 formed ina bottom member I41. .The..top and:- bottom members. I44 and I4! are connected by an annular member I48 of permanently 'magnetised vmaterial thus forming a complete circuit for the magnetic flux which traverses the annular airagap between the. pole piece I45 and the wall T of theaperture I46.

There extends withinith'e' annular air gap the. cylindrical skirt portion of a cup-shapediformer I5Il.formed from. a high conductivity metal, such. .7 as copper, and provided on its lower end face..- with a central tubular extension or bush I5 I having ,a reduced. dia'meterouter end whichis secured in amaperture in a flat resilient strip 152 by means of a collar I53l'secured onthe reduced diameter portion of the .bush I5I. 'Withinthe. inner. endof the aperture through the bush I 5I is engaged a bush I 54 of insulating materiaLwithinwhich is engagedasa close fitthe reduced end of a.spindle(l55 which extends axially with clearance. :through the bore in the centralcore piece I43. 1

At. the L-encL remote vfrom the former I50 the.

strips... 1.5.2 endnI 51 1(see .forhexample, Figs, .10 and- 11) are disposed radially with respect to the axis of the spindle I55 and have their outer ends secured on the upper face of the member I44 and on the lower face of the member I 51, respectively. The mounting of the strips is effected with the aid of blocks of insulating material indicated generally at I so that the strips are electrically insulated from the members I44 and I41. Due to its method of mounting, the spindle I may move axially without any substantial movement in a direction transverse to its axis and a practically frictionless straight-line guidance for the former I50 is thus ensured.

A coil I59 of insulated wire is wound on the skirt portion of the former I50, the one end of the coil being connected electrically at I60 to the spindle I55 and the other end of the coil being electrically connected at IE! to the bush I5I forming part of the former. It will be seen that the coil is electrically connected between the strips I52 and I51, it being understood that the spindle I55 and the tubular element I 56, and also the strips concerned, are of electrically conducting material. The electric signal to be utilised in the coil I59 is fed in by way of electric leads I62, I63 which'are respectively connected, in a connector plug I64 (Fig. 11) to further leads I65 and I66 which are in turn connected to lateral extensions I52a and Him formed on the respective resilient strips I52 and I5! On the upper face of the top member I44 of the pot-type magnet is secured a block I61 having a recess I68 centrally of its underside into which extends the upper end of the spindle assembly and the inner end of the strip I51. Centrally of this recess, there is formed a bore to receive a plug member I69 having a bore I10 formed axially thereof from its lower face. the mouth of this bore being flared to constitute a conical valve seating I1I with which co-operates a ball valve I12 which is supported by an abutment I13 of a non-conducting material, such as. glass, which is firmly fixed in the upper end of the bore in the tubular element I 56. Similarly, on the lower face of the bottom member I41 of the magnet structure there is secured a block I14 having a stepped recess I15 formed centrally of its upper face to receive with clearance the lower end of the coil former I50 and the downwardly projecting extension I5I thereof. Centrally of the base of the recess I15 there is formed a bore to accommodate a plug member I15 from the upper face of which is formed an axial bore I 11 having its upper end flared to constitute a conical valve seating I18 with which co-operates a ball valve I19 contacted by an abutment member I89 of insulating material, for example, glass, which is firmly fixed in the lower end of the bore in the extension I5I on the coil former I50.

In the end face of the block I14 there are secured connectors for three pipes IBI, I82 and I83, the first of which, IBl, is adapted to supply compressed air to a horizontal bore I84 formed in the lower part of the block I14 parallel with one of the longer sides thereof. The inner end of the bore I84 communicates through a short transverse bore I85 with the lower end of a vertical bore I95 formed from the upper face of the block I14 and having its upper end enlarged to receive the lower end of a tube I81 which passes through an aperture in the bottom member I41 of the magnet structure and through an aperture in the top member Hit of this structure to have its upper end received in the enlarged lower end of a vertical bore I 88 formed from the underface of the block I61. This bore I88 at its upper end opens into a horizontal bore I89 which leads.

to the bore in which the plug member IE9 is fitted, this plug member having a radial bore I90 of much reduced cross-sectional area formed therein to establish communication between the bore I 99 and the bore I 10 formed in the plug.

There is also formed in the plug member I99 diametrically opposite to the bore I90 a further radial bore I9I adapted'to establish communica-.

tion between the axial bore I10 and a continuation I92 of the bore I89 which is plugged at its outer end as shown at I93. Intermediate the length of the bore I92, there opens thereinto a transverse bore I94 which, at its other end, communicates with the upper end of a vertical bore I95 formed from the lower face of the block I61 and having its lower end widened to receive the upper end of a tube I99 which passes through apertures in the top and bottom members I44 and I41 of the magnet structure to have its lower end received in the widened upper end of a bore I91 formed in the block 914 from the upper face thereof. The lower end of the bore l91 opens into a horizontal bore I90 which leads to the connector at which is attached the pipe I32.

Returning now to the plug member I16 in the lower block IM, it will be seen that this is formed with a radial bore I99 of restricted crosssectional area which is adapted to establish com munication between the axial bore I11 and a horizontal bore 290 which is formed in the block 114 to open into the lower end of the vertical bore I86. The plug member I15 is also formed with a radial bore 20I which is arranged to establish communication between the bore 511 and a further horizontal bore 202 which leads to the connector at which is attached the pipe I33.

Referring to Fig. 12, it will be seen that the tubular element I56 has secured therein the inner end of a radially extending rod 293 to the outer end of which is attached the lower end of a coil spring 204, the upper end of which is attached to a stud 205 secured approximately centrally of the length of an adjusting arm 205 which is pivoted at one end on a bolt 201 (Fig.

' 10), around which is disposed a mouse-trap-type spring 208 adapted to urge the arm 200 in the upward direction so that it will tend to extend the spring 204-. The other or free end of the 1, arm 209 is arranged to be engaged by an adjusting screw 209, rotation of which can be utilised to depress the arm 206 against the action of the spring 208. It will be appreciated that by this means the supporting force exerted by the spring 204 upon the spindle !55 may be adjusted,

'- whereby the zero indication of the instrument 'vided due to the former I 50 being composed may be correctly set.

The manner in which the apparatus illustrated in. Figs. 9 to 12 is adapted to operate will be clear- 1y understood from the foregoing description, it merely being necessary to state here that when the signal current is caused to flow through the coil I59 wound .on the former I50 a proportional force is exerted upon the spindle I55 tending to move it axially and that this movement is assisted by the pressure acting upon one of the ball valves I12 or I19 and resisted by the pressure acting upon the other of the ball valves. It will be understood that an equilibrium position may be reached in which the diiference between the pressures in the two pipes I 92 and IE3 is proportional to the value of the electric signal received. It should be noted that efficient damping is proof high conductivity material.

aneaaca Wi'tliizamarrangementz as thus idescribedzcit; is possible-rte utilise-an electric; signal oi. lverylgiow: intensity-mo cause:.theaproductiomof a relatiyely large/pressure. difierenceiorza :certain rate of flowof therompressed 'air through the. corresponding 5, passages; the. ratio between: the power of: theinput Signak'anctathe power output: being. as :h-ighi: as 1:4001' Moreover, the relationshipxbetweeninput; signal'sand; output pressure-is of a linear/char:- actenrtr: c

In: a modification of. the apparatus! illustrated in..Figs. 9 to l2,. the-.spindle;ls55 maybe of a mag-n netisable material 1andt..'provided withaan xeccerr-r: trio enlargement at each Send..- so arranged that theimagnetic fluxithrouglrathe' spindle lWilli' pro-1 l ducei a; radial iorceactingzupon the: latterzin the, direction for: tensioning the.;fiexible:i.stripsw 4-52: and [51s. employed ior;supporting'zthecspindleand: coil carrangement; This modifications illusi-L trated: in Fig-.213 where: the spindlei 1.55.. is'showni' provided withi v eccentric enlargements 1555a "dis-1 posedm oneaadjlacent each-fendihereof; with the ma inzma'sslof the imetal' in each enlargement dise POSEdfitd that side of the axis-of the spindle which is remote fromz-theranchoring pointsfonthestripa a5.

sourcenindicated ias; :a battery: 2 12;; 7 Above the;

slide. wireizl 0- is. located. a. contact strip: 2] 3: be tween which :andi:.the. ."slidesr wire is 'disp-osedca member) 2:! 4 carryingfl electrically interconnected" contacts M5 and 216 .zarnangedl respectrvelyszto wipe'the 'fsli'dei wire 21:0 ahdathe contact stripf2-l'3. Beneath the! slidewiraZ-is is; disposed a l further: contact strip: 2H; betweemiwhichxandiztheaslidei wire dispose'ci atnormally"stationarypwipers'mlaiir adapted: ztomake contact betmeerrathetwontacto .5.

strip: 2J7: and: anaappzzopriate.pointzonrthea-slidei wire. 21 0;: :;The\ contact:sstripsai 213 sandal! L are. connected by electricsleadssto. thefinput: leads tB'Z" and 153i of: Janiz el'ectricr signaleto-pressurew verter -suchas has :been edescribed 'witlrf;refer-. ence to Figsx 91th "12 an 's'indicated generallyt by thereferenoe 2 is in Fig? 14.1 iFor the purposem of illustrations the putput pipeswl 82 landdi fii mi this concerter'are showmas connected to themes-x spective manometer 1 2 2 03 The 5 supply piipei to the cons verteri's showrr at =18 I 1 i" In this arrangement themembe1 2W is; con- 1 nectedxmechanically tothe" displaceablerelen'ientg themotionof'wh-ich='isto be*represented as a 6O proportional dii'rer'ential pressur'eand "movements of -the member cause signal currents i of "various intensitiestolbe transmitted to the 'conyerte 219 in .a. manner whichwill"be well-pnderstod By? reason rof theprovisi'on of tlle'wipei 21 8 it pos sibl'e for these' currentsato' vary insignand fur thernrore fon'the zeronpoint et the complete ap paratus to be readily adjuste'dn? Theiadjustmentioi the zerorpoint in apparatus" according: to thee-invention; tthatflistoi sayrthez. adjustmentvnf theipressnrezor pressure-difference: whichuis produced ion a; zero .yalue rot the variable force 'mayzbe sefiected, asahas'zjus TPbeem mene-r tinned;by'imeanarforct djusting-z;.the ositionxofi ends": I of thew -U-tubalmf' a a mercury 55 ofhthetfslidewirearrangement; showmin 2Eig'.i;:14 or'it maybe .efiec'ted in .thecther forms: of ap-v paratus described by applying anadjusting force to the abutment which is adapted. to actnupon the ball valve. or ball valves, for example;v through the intermediary of a'springwhich. may be ten-" sionedi- 'to the-required degreefsee forexample, Fig.'1:2 Thesexadjustments of the. zero-point. do notualter the slope of the. input signals-output pressure characteristic. but: this slope may. be: altered if:- desiredyby making provision :for varye ing lever arm'ratios. in those constructions ems ploying. levers for applying the force to the ball or balls; or by connectingresistances in series'or in parallelwith the coilof the. electric 'signaletoi pressure converter.

It is: to be understoodthat more thant one' arrangement;.:in accordance with. they-inventionmay be provided and connected in cascade where: much higher power-amplifications :are required: A similar:resultfimayibe obtained :by'thewuse "of feedsback: arrangementsa-In the case of the, casca'dcxarrangement, any :of the-formant the: inventicn which :have been described above-may serve as the first' stage according to 'thenaturea' of ."thellxprimary or'rinpuir signal. The output;v pressures or pressuresrliiiferfences derived :from: the first stage may then :be fed as secondary sig- Tia-1S: into :a pressurez-to-pressure converter; for:

example, of 'thev'bell-type' referred to above; ".It is easily possibleby utilising an electricaksi gnale: to-pressure converterras a? first-stage with a bell-; type pressurez-to-pressure: converter as a secondstage to obtainpower amplifications of the' order of 1,000,000.:19

An example: of a;' cascade arrangement; such was hasjust been mentioned is illustrated in Fig; 1-5.: In thisarrangement, the electrical-leads:221 sup ply the electrical signal", to. an electrical signal? topressure'z' converter: 222. constructed 7 as: describedaxwith reference .to Figs 9 to '12 and the output-pressures in the pipes I82. and I83 derived from'itheinputrpressure in the pipe l8! are supplied tothe-interior spaces of thexbells' 223 and 22A: of a bell-itype pressure-to-pressure converter. Thesecbells-"act upon-opposite ends of a lever 225 which, is pivoted :at 226; on sa fixed support and carries. at opposite ends .abutments 22'! and. 228= which :act'cupcn the. respective" ball :valves '2 2 9 and 23 0 401 two-: basic devices of \theicharacter' describediswith-s reference 'to 'Fig; 1. These'rball valvesxcontrol outlet p'assages. 23lj and:232 'from' the respective chambers 233 and 234. whichare in iturnxfed *throughithe restricted passages 235 and 23 6 fromtarcommonsupply'fll of compressed airs The;outlet.;pipes':238 and 239"from the respective;=chambersa-233 and dare showmrfor' illustration purposes only; as connected to the re spectivexendsi of lthe U-tube of 5a mercury"ma-'- nometer 124a; I The; operation: .of .thisapparatus J will he Frea'dilyiun'derstood from thetbregoing-dew scriptiona Figf lfi illustrates anexampie of a feed-hack arran ement I in which: an: electricalu signal-tm pressure: 1 converter, '1 which i v is diagrammatically indicatedat 25!, has its snindlel iz mecliani calla? linlredvto the iover 263 of a pressure-topressure converter of the belbtype. The pressures in the. respective output pipes- 24 l and 24'5 of thecomzert 2241i supplied beneath'the-bells- Mfi andv-M'imvh ,h are secured to the'lever 243 at either; side; :oi: the" pivot- 248 i for a the latter.- The? ontl'et pipesniiti and flw are also continued beyondrthesbranches. which 'lead to the interiors thciz'normaiiy stationaryszwipenzflfi inaitheof the belisxto a point; whichaha-differential l5 pressures are tobe utilised. It will be seen that with this arrangement, the bells are subjected to the pressures developed in the electric signalto-pressure converter and that the corresponding forces on the bells are fed back to the spindle of the signal-to pressure converter.

In another form of feed back arrangement a second force acting on the abutments contro line the ball valves is introduced in such a way that a linear or semi-linear relationship between abutment displacement and force is secured with a negative slope characteristic. For example, in the electric signal-to-pressure converter a strip of soft iron may be secured to the spindle to extend radially therefrom and two permanent mag-- nets may be provided to act upon the strip in opposition the sense for producing axial motion of the spindle. The arrangement is normally such that the central position of the spindle the forces acting upon the strip due to the attractions of the permanent magnets will just balance. Consequently when the spindle and strip move away from the central position there is a resultant magnetic force tending to increase the original displacement. be obtained by using one magnet in combination with a spring or weight bias.

- In the apparatus comprising pivoted levers carrying the abutments for the ball valves and adapted to have the force which is to be converted into a proportional pressure difierence applied thereto, several examples of which have beed described, the force has been considered to be variable in magnitude and applied to the lever at a constant distance from its fulcrum. It

is also possible in certain applications to reduce a pressure having any one of a number of predetermined relationships to a force of substantially constant magnitude by utilizing what is in effect a pivoted lever and varying the 1305i' tion of the fulcrum or? the lever in the manner required to produce the desired relationships. An example of an application of such an apparatus is in the proportioning of an output pressure to a given input pressure so that, depending upon the setting of a movable part in the apparatus, the relationship between the two pressures will have a desired value which will be maintained irrespective of small variations in the value of the input pressure. An example of an apparatus adapted for use in this application is illustrated in Figs. 17 to 23 and will now be described.

As shown, rectangular block 249 is formed with a central screw-threaded bore 25% within which is secured a vertical pivot member 251 having an enlarged head 252 on its downwardly projectin end. A base plate 253 of the same dimensions as the block 2% is spaced from the lower face of the latter by a cylindrical wall 254. the base plate and the'blocl: being secured to each other by bolts 255 so that they will clamp the wall 255 between them. The pivot 25! extends axially into the cylindrical chamber thus provided and terminates short of the base plate 253 into which is secured the upper end of a spindle 258 which is rotatably received within a central. hub 25? formed on a dial plate 258 having a depending peripheral skirt 258 and formed around the upper edge of the latter with a series of teeth 2%. The spindle 2513 projects below the hub 257 to have secured thereon by means of a grub screw 26! an abutment collar 262 between which and the underside of the dial plate 258 isdispcsed around the hub 251 a helical com- Similar effects can pression spring 263. Below the collar 252 the spindle 255 has rotatably mounted thereon a toothed segment llt l which is retained on the spindle by means of a nut and washer as shown. Secured upon the upper face of the segment 26 i is a pointer 265, the upturned free end of which is disposed to co-operate with the skirt on the dial plate. The teeth of the segment 254 are in mesh with corresponding teeth on an adjusting element 266 which may be moved when desired in order to rotate the pointer 2% relative to the dial plate when small adjustments of the zero position or the instrument are required.

' The block will is adapted to be fixed in position upon the rear face of a suitable panel (not shown) by means of screws or bolts entering the screw-threaded recesses 25? shown in Fig. 22, the

portion of the dial plate in the immediate vicinity of the pointer 2th projecting through or being visible through an aperture formed in the panel and the adjusting element 256 being suitably mounted so that it may, when required, be moved in the one or other direction to cause slight rotational movement of the pointer 265 relative to the dial plate. On the upper face or the latter, there is formed. an annular upstanding rib 268 adapted to contact the underside of the base plate 253 under the pressure of the spring 263. It will be appreciated that the dial plate is thereby held frictionally in position but may, nevertheless, be rotated relative to the base plate and the spindle 256 when required, for example, by means of a toothed wheel meshing with the ring of teeth 269 on the dial plate. Alternatively, the ring of teeth may constitute knurling so that the dial plate may be rotated directly by hand. It will be understood that, although not shown, suitable calibrations will be marked on the skirt of the dial. plate to co-operate with the pointer 265.

A sleeve 269 is rotatably mounted on the portion of the pivot ZEI which projects into the cylindrical chamber bounded by the wall 23d and has fitted over its lower end the central boss 2i!) of a support member 2?! which is of substantially T-shape in plan View and has the boss disposed in the shank portion adjacent to the cross-piece. The support member is secured to the sleeve, for example, by a ring or solder 2'12. Qentrally of the width of the free end of the shank portion of the support member 27! there is secured a knife edge 2'53 and centrally of the width of the free outer edge of the cross-piece portion of the member there is secured a corresponding knife edge 214, the supporting edges of the knife edges being upwardly directed and located in the same horizontal plane as parts of a diameter passing through the axis of the pivot 25L Towards each end of the cross-piece portion of the support member 2', there is formed in the upper face a cylindrical recess 275 (see Fig. 18).

A plate 216 of a rigid material is shaped to present a substantially semi-circular portion joined at the centre of the length of straight edge by a rectangular projection, the dimensions of the plate, which is completely flat, being such that it will fit within the wall 254 with a small but adequate clearance when engaged over the sleeve 269 by means of an aperture 2T! formed in the plate concentric with the circle of which the arcuate edge or the plate 2% constitutes a part. There is a small clearance between the wall of the aperture-2i? and the outer surface of the sleeve 269 so that the plate may'rock slightly about an axis which coincides at one end with the disposed slot 294 (see Figs, 18 and 20).

medial line of the rectangular extension on the plate. On the underside of the plate there are secured two rectangular elements each formed on its underside with a V-section groove adapted to receive one of the knife edges 213, 214. The one rectangular element 218 is fixed to the central portion of the arcuate edge of the plate 215 so that the knife edge 213 may engage in the V-shaped groove 219 of this element whereas the other element 280 is fixed at the free end of the rectangular extension on the plate 215 so that the knife edge 214 may engage in the V-shaped groove 28! of this element. The cross-section of the grooves 219, 28!, is such that the plate 215 may rock on the knife edges to a small extent. In order that the plate may not become accidentally dislodged from the knife edges it is formed at the appropriate locations with extensions 282 and 283 (see Fig. 21) which extend downwards, from the corresponding points on the plate,.outside the knife edges and are then turned inwards under the latter.

Secured transversely of the rectangular projecting portion of the plate 215 is a cross-piece 284 the ends of which are located above the centres of the cylindrical recesses 215 formed in the cross-piece of the support member 21!. On each end of the cross-piece 284 there is secured a disc 285 (see Fig. 23), which is of a diameter slightly smaller than the diameter of the corresponding recess 215 and it attached to the cross-piece by a short rod 286 which passes through an aperture formed in a cover plate 28'! secured in position over the corresponding recess. As will be understood, the discs 205, in conjunction with the recesses 215, constitute air dash-pots.

The boss 210 of the support member 21! is formed with a radially extending arm 20B having its centre line set at an angle of 90 to the axis containing the knife edges 213, 214, and is formed from its free endwith a slot 203, within which is engaged as a close sliding fit a pin 290 upstanding from about the centre of length of a lever 29! which at one end is pivoted on one of the bolts 255, suitable tubular distance pieces 292 and 293 being engaged over the bolt as shown in Fig. 20. In order to accommodate the movement of the lever 28! and to permit the mounting thereof on the appropriate bolt 255, the wall 254, is formed with an appropriately The free end of the lever 29! is formed with a longitudinally directed slot 295 within which is engaged as a close fit a pin 295 which is secured at its lower end, asby a nut 25'! (Fig. 1'7), in the dial plate 258 at a predetermined radial distance from the axis of the spindle 255. In order that the necessary rotation of the dial plate relative to the base plate 253 may be effected, the base plate is formed with an arcuate slot 258 through which the pin 296 extends. The proportions and dispositionsof the arm 288 and lever 29! are such that there is a predetermined relationship between the motion of the dial plate and the consequent motion imparted to the support member 21! through the intermediary of the pins 295 and 290and the lever 29! and arm 288. It will be seen upon considering Fig. 18 that for the position of the parts indicated, rotation of the dial plate 258 in the clockwise direction relative to the base plate 253 will cause the lever 29! to rock in the clockwise direction about its pivot 255 and thereby to move the pin 230 along the slot 289 in the arm 288 to impart a much reduced anti-clockwise rotation to the support member 21!.

Returning now to the block 249 and referring more particularly to Figs. 17, 21 and 22, it will be seen that three connecting points for fiuid pressure conveying pipes are provided along the face of the block which is opposite to that face in which are formed the mounting apertures 261. The first of these connecting points is marked 299 and is connected by way of a passage 300 to a transversely directed passage 30! which is plugged at its outer end as shown at 302 and at its inner end communicates with a vertically directed bore 303 formed from the underside of the block 249 and enlarged at its lower end to receive an axially bored plug 304 having a ball valve 305 engaged in its bore as a close sliding fit. The bore, as can be seen from Fig. 17, has a cylindrical wall. The spacing of the lower end of the plug 354 from the upper surface of the plate 2'56 is such that the ball normally rests upon this surface with its horizontally disposed great circle located just within the mouth of the bore in the plug. As can be seen from a comparison of Figs. 17, 19 and 22, the disposition of the ball 305 is closely adjacent to the pivot 255 as indicated by the dotted line position shown in Fig. 19.

The second of the connection points is marked 355 in Fig. .22 and is connected by way of a passage 351 into a transverse passage 308 which is closed at its outer end by a plug 309 and opens at its inner end into a passage 3i0 which in turn opens into a vertical bore 3!! formed from the underside of the block 249. Within this bore is secured a tubular plug member 3!2, the bore 3l3 of which is flared at its lower end to constitute a conical seating 3 !4 with which cooperates a ball valve 3!5. As in the case of the ball 305 the spacing of the lower end of the plug member 3!2 from the upper surface of the plate 216 is such that the ball 3 !5 will rest on the said surface while its horizontal great circle is disposed approximately at the level of the mouth of the. conical seating 3!4. Communication is established between the passage 3!!! and the axial bore tilt in the plug member 3!2 by way of a radial bore 3E5 formed in the plug member and having a restricted cross-sectional area. At a location opposite to the bore 3I5 the plug member is formed with another radial bore 3!1 which opens into a recess formed between a flat on the plug and the wall of the bore 3H, this recess being in free communication with the third of the connection points referred to above, which is indicated by the reference 3l0.

In the operation of the apparatus illustrated in Figs. 1'7 to 23, a supply of gaseous pressure fluid is connected to the connection point 299 and therefore exerts through the ball 305 a certain force upon the plate 215, this force being strictly proportional to the value of the pressure of the fluid supplied at 299. Since, with the parts disposed in the positions in which they have been illustrated in the drawings, the ball 305 is located at a small distance from the axis about which the plate may tilt, there is a tendency for the forces exerted through the ball to tilt the plate.

At the connection point 306, there is supplied a gaseous fluid under pressure which may have any desired value in relation to the pressure of the fluid supplied at 299. This pressure is applied to the ball 3!5 which, in the initial position of the parts, is located substantially on the axis joining the knife edges 213, 214, as indicated by the dotted circle in Fig. 19. Since with the parts in the position shown, the ball 655 is held in 'sea'ling contact with the seating the pressure supplied at 306 is "fully available at the connectionpoint 3H3. If, however, the support member 211 "be rotated through a small angle aboutthe axis-of its pivot'25l it will be seen that the force exerted through the ball 3!? upon the plate 216 will now have 'a cer'tain moment. The force exerted upon the plate through the ball 305 also has-a certain "moment and it will be appreciated thereforethat the plate 216 thus becomes in'eflect'a lever with arms of unequal length and thata position of equilibrium will'be reached in themanner already described in the foregoingso 'that the pressure available at the connection point '3 [8 will now be in 'a ratio to the pressure supplied at the connection point 299 dependent on the ratio of the lengths of the lever armsi. e. the distances of balls 315 and 305 from the tilting axis represented by the knife edges 213 and'Z-M. The 'ratio'ofthe pressures can be'variedby rotatingthe-member 2' about its axis 251 by rotating the plate 258, the motion of which is transmitted-by linkage 296, 295, 290, 289 to member 2'H. Thislinkage'is vpreferably so dimensioned that the pressure ratios'can be read on a'logarithmic scale on the skirt 259 of the member258. It will be clear, Without further description, that by "suitable calibration of the apparatus, it willbe possible toensure that the'pressureavailable at the outlet 313 will bear a 'specifledrelationship to the pressure supplied at the inlet 289.

'It will be appreciated that the tilting motions of theplate Z'lB are of relatively small magnitude and that the dash-pot arrangements carried on the cross-piece of the support 'member 21! willprovide the necessary degree of positive damping to ensure that the apparatus will :remain stable throughout its range ofadjustment.

What I claim is:

1. A.plurality of means each adapted to produce a fluid pressure proportional to the value ,of a variable input'force and arranged in successive stages, means adapted to sup ly the proportional pressure produced in the lower of two successive stages .to the higher of these two stages, and means associated with each stage above the lowest stage for converting 'thepressure sup lied thereto into. a proportional variable input force for that stagein which-the means in each stage for converting 'the input 'force into a proportional pressurecomprisesa duct having a constricted-outlet, a supplyof fluid for maintaining a substantially.constant'pressure in said duct, a space containing fluid -maintained at a pressure lower than said constant pressure, a chamber having "an ioutlet'ito said space and supplied withfluidrirom said duct by Way of said constricted outlet so that a-pressure will be produced in said :chamber'which varies withthe rate at which fiuidescapes therefromibyiwayof thesecond-mentioned:outlet, a coned valve seating disposed around the second mentioned outlet, 'means for causing a force bearing a given ratio to the instant value of the variableforce constantly to urge an element-towards said seating, a ball interposed between said element and said seating and constantly urgedla'way from the latterby-the fluid escapingfrom the secondmentioned outlet, the sizes of the ball and the second-mentioned .outlet being so determined in relation to said constant pressure that the maximumforce capable .of beingtexerted upon theball by the escaping fluid is at least equal to the 5 to, and of the same-'signaaa variable input 'af'orce capable of assuming both positive and negative values and each comprising a supply of fluid under substantially constant pressure, two chambers, two ducts each connected "between the said supplyand onecfthe chambers,

a constriction in each duct through which-the pressure fluid can pass tothe respective chamber, a space surroundingthe chambers andcontaining fluid maintained at a pressure Flower than the supply pressure, an-opening in each chamber for establishing communication between the chamber and the said spaceya'cone'd valve seating disposed around each such opening, a ball valve associated with each seating F andurgedaway' from the same under the action of pressure fluid escaping through the associated openings and means -'for applying'the variable input'force to the said balls in opposite senses so "that it will urge the one ball into sealing '25 contact withits associated'coned seating while permitting the otherball to move awayfromits associated seating and vice verse, the sizes of the balls and "the associated-openings being so determined in relation to the supply *pressure that the maximum force capable pf being exerted upon any ball'by the-escapingfluidis at'least equal-to the maximum value of the'variable input'force, combined-with means fOTlltiliSiIlg the proportional pressure difference pro duced in one such converting means for producing the --variable input force for another such converting means whereby all the converting "means are connected in cascade.

3. Means for operating a pressure responsive e40 devicein accordance With-a pressure "difference proportionalto "a variableinput-force capable of assuming-both positive and negative'valuea-comprising a supply 'of fluid "under constant pressure, a first 'ductya "firstconstricted outlet conmeeting said first duct to said supply, a body of fluid maintained at "a "substantially "constant pressure the magnitude of which is lower "than that of'theconstant pressure of said supply, a first outletestablishing communication between said first duct and said body of "fluid so that afluid pressure will be produced in said first duct whichvaries withthe 'rate'at which fluid escapes byway'of said outlet, a first'cone'dvalve seating disposed around said first "OllflQtf'fi/fiTSt element movable towards and away "from"said second constricted outlet connecting said "second duct to said'supply, a second .outletmcn- 'necting-said second duct to said body pf-fiuid so that a fluid-pressure willbe 'produced-insaid second duct which varieswith'the'rate'atwhich fluid escapes by way of said second 'outlet,:a

second coned valve seating disposed'around said second outlet-a second elementmovabletowards and 'away from said second seating, -a second ball interposed between saidsecondelement and said second seating-and 'constantly'urged away -fromthe Iatter by-thefiuidescaping from said 'second'outlet, and-means for applying a force .bearing a'given ."ratioto thevariableiforce;simultaneouslyto.saidrfirstrelementzand toesaid second ;';;5 element so as toiurgerzsaid.rfirstirballitowardszsaid first seating while permitting said second ball 21 to move away from said second seating and vice versa, the variable pressure produced in said first duct and the variable pressure produced in said second duct being applied to said pressure responsive device.

4. Means according to claim 3, wherein a device is provided for applying positive damping to the force-applying means.

5. Means according to claim 3, wherein the force-applying means comprises an electro-magnetic device adapted to convert an electric signal into a proportional force.

6. Means according to claim 3, wherein the proportional pressure difierence produced is caused to react upon the force-applying means in the sense to tend to vary the value of the pressure difierence.

7. Means according to claim 3, wherein said first element and said second element are rigidly connected to each other.

8. Means for operating a pressure responsive device in accordance with a pressure difference proportional to the magnitude of an electric signal capable of assuming both positive and negative values, comprising a supply of fluid under constant pressure, a first duct, a first constricted outlet connecting said first duct to said supply, a body of fluid maintained at a substantially constant pressure the magnitude of which is lower than that of the constant pressure of said supply, a first outlet establishing communication between said first duct and said body of fluid so that a fluid pressure will be produced in said first duct which varies with the rate at which fluid escapes by way of said outlet, a first coned valve seating disposed around said first outlet, a first element movable towards and away from said first seating, a first ball interposed between said first element and said first seating and constantly urged away from the latter by the fluid escaping from the first outlet, a second duct, a second constricted outlet connecting said second duct to said supply, a second outlet con necting said second duct to said body of fluid so that a fluid pressure will be produced in said second duct which varies with the rate at which fluid escapes by way of said second outlet, a second coned valve seating disposed around said second outlet, a second element movable towards and away from said second seating, a second ball interposed between said second element and said second seating and constantly urged away from the latter by the fluid escaping from said second outlet, means for converting said variable electric signal into a force the magnitude of which is proportional to the magnitude of said signal and means for applying a force bearing a given ratio to said proportional force simultaneously to said first element and to said second element so as to urge said first ball into sealing contact with said first seating while permitting said second ball to move away from signal capable of assuming both positive and negative values, comprising a supply of fluid under constant pressure, a first duct, a first constricted outlet connecting said first duct to said supply, a body of fluid maintained at a substantially constant pressure the magnitudeof which 1 22 is lower than that of the constant pressure of said supply, a first outlet establishing communication between said first duct and said body of fluid so that a fluid pressure will be produced in said first duct which varies with the rate at which fluidivith the rate at which fluid escapes by way of said secondoutlet, a second coned valve seating disposed around said second outlet, a second element movable towards and away from said second seating, a second ball interposed between said second element and said second seating and constantly urged away from the latter by the fluid escaping from said second outlet, a connecting rod rigidly connecting said first element to said second element, means for converting said electric signal into a force the magnitude of which is proportional to the magnitude of said signal, and means for applying said force axially to said rod simultaneously to urge said first ball towards said first seating while permitting said second ball to move away from said second seating and vice versa, the variable pressure produced in said first duct and the variable pressure produced in said second duct being applied to said pressure responsive device.

10. Means for operating a pressure responsive device in accordance with a pressure difference proportional to the magnitude of an electric signal produced by a given source of such signal, said signal being capable of assuming both positive and negative polarities, comprising a supply of fluid under constant pressure, a first duct, a first constricted outlet connecting said first duct to said supply, a body of fluid maintained at a substantially constant pressure the magnitude of which is lower than that of the constant pressure of said supply, a first outlet establishing communication between said first duct and said body of fluid so that a fluid pressure will be produced in said first duct which varies with the rate at which fluid escapes from said outlet, said first outlet being arranged to direct said escaping fluid in a given direction, a first coned valve seating disposed around said first outlet, a first element movable towards and away from said first seating, a first ball interposed between said first element and said first seating and constantly urged away from the latter by the fluid escaping from the first outlet in said given direction, a second duct, a second constricted outlet connecting said second duct to said supply, a second outlet connecting said second duct to said body of fluid so that a fluid pressure will be produced in said second duct which varies with the rate at which fluid escapes by way of said second outlet, said second outlet being spaced from said first outlet in said given direction and being arranged to direct the fluid escaping therefrom in a direction coaxial with and opposite to said given direction, a second coned valve seating disposed around said second outlet, a second element movable towards and away from said second seating, aball interposed between said second element and said second seating and constantly urged away from the latter 

